Kirk,
I've found a few articles that explain it this way:
"Good acceleration requires a rich mixture, but SUs have no accelerator
pump. To compensate for this, the piston damper slows the piston's rise
when you step on the gas. This temporarily increases air velocity over
the jet and draws more fuel, thus enriching the mixture. The effect is
only temporary, returning to a leaner condition for cruise."
See the two URL's below for reference, and search on 'accelerator pump'.
It is also stated that you can 'increase' the accelerator pump action, by using
thicker oils in the su dash pot, to delay 'piston rise'.
http://www.mossmotors.com/forum/forums/thread/11209.aspx
http://books.google.com/books?id=CTz2EAp2ua8C&pg=PA67&lpg=PA67&dq=su+accelerator+pump&source=bl&ots=gs0qmgqIhH&sig=gemAmGKVzLTg0r4jSoQ1KOIAt3w&hl=en&ei=5iukScaPBqCSsQPpxNiwAg&sa=X&oi=book_result&resnum=6&ct=result
Regards,
Bryan Vandiver
59 bugeye
San Jose, CA
--- On Mon, 2/23/09, Robert E. Shlafer <pilotrob@webtv.net> wrote:
From: Robert E. Shlafer <pilotrob@webtv.net>
Subject: Re: [Spridgets] SU Question - Accelerator Pump Question
To: "Bill L" <pythias@pacifier.com>, "Kirk Hargreaves" <khargreaves2@gmail.com>
Cc: spridgets@autox.team.net
Date: Monday, February 23, 2009, 6:51 PM
Purrfect! :)
Cap'n. Bob '60 :{)
-----Original Message-----
From: Bill L
Sent: Monday, February 23, 2009 5:05 PM
To: Kirk Hargreaves
Cc: spridgets@autox.team.net
Subject: Re: [Spridgets] SU Question - Accelerator Pump Question
Hello Kirk,
It has to do with the rate of rise of the piston. ...
the carbs operate atmospherically. when you press on the pedal, you're
opening the butterfly valve. This allows the engine to SUCK more. ..the
There is an air channel that is arranged so that when this suck is
increased, the piston to which the needle is attached rises, allowing both
more air, (from the air cleaner) and more gas (because you've pulled
the
needle out of the jets) to flow. You can't flood the carbs because
they
only deliver as much air/fuel as the engine will suck...
no to the point. the oil in the damper limits the RATE of rise of the
piston. This limits the amount of air that can flow sucking relatively
more
gas from the jet, causing an increase in the richness of the mixture
during
acceleration. When the engine again achieves relative equilibrium the
distance of the piston out of the jet (and thus the amount of gas flowing)
and the flow of air are stoichiometrically in balance. (theoretically)
if this isn't true someone will, i'm sure, correct me. .. PLEASE!
--
Best regards,
Bill L. mailto:pythias@pacifier.com
'66 Sprite MKIII HAN8L49403 "the red thing"
Taken as a whole, the universe is absurd
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